This invention relates to an impact drilling tool and, more particularly, to a pneumatically actuated impact drilling tool for rotary drilling having a center feeder with a shuttle valve located thereon for causing reciprocating action of a hammer against an anvil to create an impact force on a drill bit.
The present invention is an improvement over U.S. patent application Ser. No. 507,968 filed on Sept. 20, 1974 and has the same inventor and assignee as the present invention, which patent application is hereby incorporated by reference.
In alternative embodiments, the present invention may be used to modify existing pneumatic drilling tools to increase their effectiveness by shifting the valving position of at least one of their pressurization or exhaust functions, above or below the hammer. A typical example can be found in the Megadril manufactured by Mission Manufacturing Company, Houston, Tex. Use of the shuttle valve on the exhaust function only would improve its performance significantly.